1. Caffeine is eliminated by liver metabolism.
2. The rate of caffeine metabolism is dramatically slowed in cirrhosis.
† Release of 14-C from labelled caffeine into the breath (as CO2) can be used as a measure for the rate and capacity of liver metabolism.
† Rate of decline of caffeine concentration in the blood (a first order elimination curve) is also a measure of hepatic function.
† Measures hepatic function directly.
3. Fasting caffeine levels are elevated in cirrhosis and correlate with residual hepatic function (most people have measureable caffeine in the blood because its presence is ubiquitous in various drinks).